ARticle | boTulInuM ToxIn A |
Figure 2 (left) (A) Father (aged 55 years) and (B) daughter (aged 20 years) demonstrate same type of idiosyncratic, asymmetric smile caused by a hyperkinetic right depressor labii inferioris. The daughter also has an asymmetric smile on the upper right, with deep nasolabial grooves and folds
Figure 3 (right)
22-year-old with an idosyncratic
asymmetric smile before (A) and 4
months after (B) 2 U of onabotulinumtoxin A, which were injected
into her right depressor labii inferioris for the second time
longer. It is best to treat an asymmetry with a lower
dose, which can be increased by a touch‑up treatment when the patient returns for his/her post‑treatment evaluation. Correcting a problem conservatively, albeit insufficiently, allows both the patient and physician to clearly assess the appropriateness of the corrective action9
. In the lower face, the muscles are small, intermingled
with indistinct borders, and do not always function in the same way in each patient. The shape and contour of the mouth and whether it is symmetrical will depend on how the perioral muscles function. When there is an obvious asymmetry, 1 or 2 u of onabotulinumtoxinA can go a long way in modifying how perioral muscles contract and interact. In one study12
, four females and
one male were treated for lower lip asymmetry. four were caused by a hyperkinetic right depressor labii inferioris, one by a left. four patients were aware of their asymmetry, which had been present since birth or early childhood. onabotulinumtoxinA was used to correct the asymmetric smile with 1–3 u. The smiles became level and symmetrical within 1 week of treatment, which lasted anywhere from 6–7.5 months with the first session, and even longer with subsequent treatments — even when using a lower dose.
Complications A thorough knowledge of the anatomy and function of the muscles is paramount when one is treating a patient with botulinum toxin A. This is particularly important when the problem is not a recognised, commonly occurring complaint with well‑established and approved techniques of treatment. Idiosyncratic or iatrogenic asymmetries need to be corrected on a case‑by‑case basis. overzealous treatment can only lead to adverse sequelae.
34 ❚ July 2011 |
prime-journal.com
Treatment implications when injecting an asymmetric smile
1Inject low-volume, 2First treatments
conservative to confirm appropriateness of treatment.
3Re-evaluate each
patient’s problem before every treatment, because the dosage of subsequent injections may change depending on how the muscle(s) respond and reanimate over time.
should be
minimal doses of botulinum toxin A directly into the belly of the muscle(s) in question.
Melomental folds Patients whose corners of the mouth chronically project downward will also commonly possess pronounced melomental folds. These superfluous folds of skin are created by deep furrows emanating away and downward from the oral commissures. When these lines extend downward along the lateral sides of the mentum, they reinforce the downward turn of the corners of the mouth, creating an inverted smile, and evoke the appearance of someone who is old. until recently, the only way to efface these lines was either by invasive surgical procedures, such as rhytidectomies, subcision and skin resurfacing, or injections of soft tissue fillers. Injections of botulinum toxin A can be given to supplement these procedures, enhancing and even prolonging their results4
.
Functional anatomy The formation of an inverted smile is produced by the hyperkinetic activity of the depressor anguli oris pulling on the lateral oral commissures14
. The muscle fibres of
the depressor anguli oris narrow as they travel upward and converge onto the angle of the mouth, where some fibres directly insert into the undersurface of the skin, while others insert into the modiolus and interdigitate with muscle fibres of the risorius, orbicularis oris and levator anguli oris near the upper lip. The lower posterior fibres of the depressor anguli oris interdigitate with the muscle fibres of the upper platysma (pars labialis) and cervical fascia that converge toward the lateral oral commissures. The function of the depressor anguli oris is to depress
the oral commissures slightly laterally and downward when opening the mouth. The depressor anguli oris is an antagonist to the levator anguli oris, risorius and zygomaticus major, displacing the corners of the mouth when it contracts in an expression of grief, sorrow, and
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